1. Field of the Invention
The present invention relates to an apparatus and a method of calibrating a print alignment error in an inkjet printer, and more particularly, to an apparatus and a method of calibrating a print alignment error between printheads of two ink cartridges in an inkjet printer.
2. Description of the Related Art
In general, an inkjet printer, in particular, a color inkjet printer, uses two or more ink cartridges. Accordingly, when an image is printed, an alignment error of an image may be generated due to an alignment error of a printhead of the ink cartridge. The alignment error of an image can be divided into a vertical alignment error and a horizontal alignment error.
The vertical and horizontal alignment errors are generated since nozzles of the printhead are not uniformly arranged and an error occurs in an apparatus for reciprocating an inkjet cartridge in a direction perpendicular to a paper path direction in which print paper is transferred.
A conventional method of calibrating the alignment error is shown in FIGS. 1A and 1B. Referring to FIG. 1, while an ink cartridge is moved in one direction, a test pattern having lines, of which intervals are set to increase or decrease at a regular pace, is printed on a paper where a reference pattern having lines at the same interval is already printed. A user selects one of the lines of the test pattern which is most aligned with a corresponding one of the lines of the reference pattern. Then, the number of the selected test pattern line and the number of the reference pattern line corresponding thereto are input to a manual calibration apparatus. A length between a reference line and the selected test pattern line is compared to a length between the reference line and the selected reference pattern line so that a horizontal alignment error is measured and calibrated. In FIG. 1A, the line 6 of the reference pattern and the line 6 of the test pattern are most aligned.
Referring to FIG. 1B, while a feeding roller is moved, a test pattern having lines, of which intervals are set to increase or decrease at a regular pace from a reference line, for example, a uppermost line of the test pattern, is printed on a paper where a reference pattern having lines at the same interval has been already printed in a vertical direction. The user selects one of the lines of the test pattern which is most aligned with a corresponding one of the lines of the reference pattern. Then, the number of the selected test pattern line and the number of the reference pattern line corresponding thereto are input to the manual calibration apparatus. A length between a reference line and the selected test pattern line is compared to a length between the reference line and the selected reference pattern line so that a vertical alignment error is measured and calibrated. In FIG. 1B, the line 6 of the reference pattern and the line 6 of the test pattern are most aligned.
However, in the conventional technology, the user needs to check a position of each line to confirm an alignment state of the test pattern. Thus, since the confirming of the alignment state of the lines of the test pattern is dependent on a visual ability of the user, a misaligned line may be selected. Also, only when the reference line of the test pattern matches the reference line of the reference pattern, calibration is possible. Furthermore, in the above method, a high resolution optical sensor is required to adopt a method of automatically calibrating alignment by using an optical sensor.